A high frequency switch circuit is a switch circuit which handles a high frequency signal (RF signal). For example, a shunt switch as a kind of high frequency switch circuit plays a role to lead the high frequency signal to the ground in a turn-on condition. In other words, the shunt switch plays a role to dissipate the RF power.
FIG. 1 shows the configuration of the shunt switch disclosed in Patent Literature 1. The ground potential is applied to a ground (GND) terminal 2. A high frequency signal is applied to a high frequency signal terminal 3. N number of transistors M(1) to M(n) are connected in series between the ground terminal 2 and the high frequency signal terminal 3. The gate of each transistor M(k: k=1 to n) is connected to the bias terminal 4. Each transistor M(k) is turned on/off according to the potential of the bias terminal 4.
When each transistor M(k) is in the turn-on condition, the high frequency signal terminal 3 and the ground terminal 2 are short-circuited (shunt) to dissipate the RF power to the ground terminal 2. On the other hand, when each transistor M(k) is in the turn-off condition, the short circuit is not formed. In this turn-off condition, it is required to suppress leakage of RF power (the RF choke) from the gate of each transistor M(k) to the bias terminal 4 as much as possible. Therefore, a resistance element (gate bias resistance) is provided between the gate of each transistor M(k) and the bias terminal 4.
In the configuration shown in FIG. 1, n number of resistance elements are disposed between the bias terminal 4 and the gate of each of the n transistors M(1) to M(n). In other words, the n number of resistance elements are connected in parallel. Typically, the n number of resistance elements are designed to have a same resistance value. The configuration that the resistance element connected with the transistor M(n) has the maximum resistance value and the resistance values become smaller gradually as approximating to the transistor M(1) is disclosed in Patent Literature 1.
Patent Literature 2 discloses a technique that a change of a high frequency current which flows through each transistor is suppressed low to reduce a the high frequency distortion. According to the technique, a plurality of gate bias resistances are connected in series between the high frequency signal terminal and the bias terminal.